1. Field of the Invention
The invention relates to a driving device for a light emitting diode (LED) module. Particularly, the invention relates to a driving device for a LED module, in which a fault detection pin has a fault notification function.
2. Description of Related Art
Along with a general trend of multifunction of electronic devices, circuits of multiple functions are integrated into a same integrated circuit or a system. To provide different power supplies to different functional circuits in the same integrated circuit or the system, a so-called direct current to direct current (DC-DC) power converter is developed. The commonly used DC-DC power converters are grouped into booster DC-DC power converters and buck DC-DC power converters.
Taking a driving device used for driving a backlight module constructed by light-emitting diodes (LEDs) as an example, such type of the backlight module drives a plurality of LED strings, and each LED string includes a plurality of LEDs connected in series. Referring to FIG. 1, FIG. 1 is diagram illustrating a conventional driving circuit of a LED module 10. The LED module 10 includes a LED string 110 and a driving device 120, and the LED string 110 includes a plurality of LEDs LED. A voltage converting unit 130 in the driving device 120 is a DC-DC voltage converter, which receives an input voltage Vin, and produces a driving voltage VDR according to a switching signal SSW provided by a switching signal driving unit 140, so as to drive the LED string 110.
The conventional driving device 120 of the LED module 10 generally has a fault detection pin Pfault, so that when a part of the LEDs LED in the LED string 110 is malfunctioned, the driving device 120 can automatically stop driving the LED string 110, so as to avoid a damage of the LED string 110 or the driving device 120 due to overheat of the driving device 120 or continuous power-supplying of the voltage converting unit 130. In other words, a comparison voltage VCP on the fault detection pin Pfault is obtained by dividing the driving voltage VDR by the LED string 110, a resistor R1 and a resistor R2. When all of the LEDs LED in the LED string 110 can normally work without malfunction, most of the driving voltage VDR is consumed in the LEDs LED, so that a voltage value of the comparison voltage VCP is smaller than a threshold voltage of a switch 150, and therefore the switch 150 is in a turned-on state. In this way, a PWM pin of the switching signal driving unit 140 can receive a pulse width modulation signal PWM_signal through the switch 150, so that the switching signal SSW becomes the pulse width modulation signal PWM_signal, and the voltage converting unit 130 can continually drive the LED string 110 according to the pulse width modulation signal PWM_signal.
Comparatively, when a part of the LEDs LED is damaged or a voltage value of the driving voltage VDR is excessively high due to other reasons, the voltage value of the comparison voltage VCP can be greater than the threshold voltage of the switch 150, so that the switch 150 is switched from the turned-on state to a turned-off state. In this way, the PWM pin of the switching signal driving unit 140 receives a ground voltage VSS through a resistor R3, and the switching signal SSW becomes a DC voltage signal (for example, the switching signal SSW becomes a logic low level signal), and accordingly the voltage converting unit 130 cannot continually drive the LED string 110, so that the driving circuit 120 may have a function for detecting fault of the LEDs LED and a circuit protection function.
However, a reason that causes fault of the LED module 10 is not only the damage of the LEDs LED, and if a circuit of the driving device 120 is damaged, it may also cause fault of the LED module 10. Therefore, when a maintenance personnel detects the fault of the LED module 110, the maintenance personnel has to detect the circuits of the LED string 110 and the driving device 120 one-by-one, and cannot obtain the damage information through the fault detection pin in the LED module 10.